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Archivum Immunologiae et Therapiae Experimentalis, 1999, 47 267–274ReviewPhage Therapy: Past History and Future ProspectsR. M. Carlton: Phage Therapy in the Past and Future
Exponential Biotherapies, Inc., 150 Main Street, Port Washington, NY 11050, USA
Abstract. Bacterial viruses (bacteriophages, also called “phages”) can be robust antibacterial agen✝ts in vitro.However, their use as therapeutic agents, during a number of trials from the1920s to the 1950s, was greatly
handicapped by a number of factors. In part, there were certain limitations inherent in pha✟ge physiology (e. g. nar-row host range, and rapid clearance from the body); in part there were technological limitations in the era(e.g. lysogeny not yet discovered); but the greatest limitation was the highly inadequate scientific methodologies
used by practitioners at the time (e.g., their failure to conduct placebo-controlled studies, to remove endotoxins
from the preparations, and to re-confirm phage viability after adding sterilizing agents to t✞he preparations). Inrecent years, well-controlled animal models have demonstrated that phages can rescue animals from a variety of
fatal infections, while non-controlled clinical reports published in Eastern Europe have s✞hown that phages can be
effective in treating drug-resistant infections in humans. This encouraging data, combin☛ed with the fact that
drug-resistant bacteria have become a global crisis, have created a window of opportunity for phage therapy to
be tested anew, this time using modern technologies and placebo-controlled designs. If successful, it can be used
as a stand-alone therapy when bacteria are fully resistant to antibiotics, and as a valuable ✍adjunct to antibiotics
when the bacteria are still susceptible.Key words: bacteriophage; phage; bacterial viruses; bacterial infections; multidrug resistance.
Phages are a kingdom of viruses that infect bacteria,
view will describe: 1) some of the key reasons this
and are distinct from the animal and plant viruses.
form of therapy failed to take root in the West; 2) its
Phages can have either a “lytic” or a “lysogenic” life
previous and current use in some enclaves of Eastern
cycle. The lytic phages are the most suitable candidates
Europe; 3) recent animal models which suggest that
for phage therapy, because they quickly reproduce
phage therapy might be useful for humans; 4) the fact
within and lyse the bacteria in their host range, growing
that the emergence of antibiotic-resistant infections has
exponentially in number in the process. Depending on
opened a second window of opportunity for phage ther-
the species and conditions, each “parent” phage can
apy; and 5) the advantages that might be gained by
produce on average approximately 200 “daughters” per
administering phages along with antibiotics, as a com-
lytic cycle. If each daughter infects and kills a host
bacterium there will be 40 000 progeny at the end of
the 2nd cycle; 8 million at the end of the 3rd cycle; 1.6
Past History
billion at the end of the 4th cycle; and so on.
Some practitioners used phages as therapeutic
agents in the West, from the 1920s to the early 1950s
A number of reviews provide details on phage ther-
(referred to hereinafter as the “historic era”). This re-
apy’s ascent and decline in the historical era1–3, 13, 14.
R. M. Carlton: Phage Therapy in the Past and Future
Table 1 Attributes of phages that tend to favor a therapeutic response
Metabolic destruction of the molecule, as it
Exponential growth in numbers, so that the
“drug” makes more of itself at the site ofinfection, where it is needed
Numerous molecules of the antibiotic are needed “All or nothing” effect: one phage particle is
to kill a given bacterium. During initiation of
therapy (and between doses), the sub-lethal dosethat bacteria “see” affords them the opportunityto express resistance genes
Antibiotics are fixed, immutable chemicals that
Phages are “living” organisms that undergo
therefore become obsolete. Bacteria that have
bacterial mutations. E. g., mutated phage tail
resisted them can pass along the resistance trait
fibers can allow binding to a mutant bacterial
receptor, or mutated phage DNA can escapecleavage by mutant bacterial endonucleases
The antibiotics in use tend to be broad spectrum, Although there are some exceptions, phages tendthereby provoking resistance in several species
not to cross species boundaries. Thus even
and genera of bacteria (in addition to the one
though the targeted bacterial species may
become resistant to the phage, it is unlikely thatother species will
We will summarize some of the more salient features
and how the problems can be overcome
Phages were discovered in 1915 by British micro-
biologist Felix Twort, and, independently in 1917,
by French-Canadian microbiologist Felix d’Hérelle.The issue. Phages tend to have a relatively narrow
Twort did not pursue his discovery, whereas d’Hérelle
host range, posing certain disadvantages. A disadvant-
systematically investigated the nature of bacteriophages
age is that one should administer only those phage
and explored their ability to function as therapeutic
strains shown to be strongly lytic for the bacterial strain
infecting the given patient. If the patient’s condition is
D’Hérelle received a fair measure of fame for his
too critical to take the time required for this matching,
discovery. He was appointed Professor of Protobiology
then one should use a grouping (a panel) of phages,
at Yale University Medical Center, and was also on the
where each of the phages therein has a broad-enough
staff of the Pasteur Institute. In 1931 he gave a series
host range that most strains of the bacterial target are
of monthly lectures on phage therapy to the New York
likely to be targeted. In his lectures to the New York
Academy of Medicine. He established phage therapy
Academy of Medicine in 1931, d’Hérelle cited the re-
centers in several countries, including the U. S., France,
ports of other colleagues whose initial trials used
and Soviet Georgia. A fictionalized account of his work
phages “off the shelf” (without being shown to be viru-
was depicted in Arrowsmith, the Pulitzer-prize winning
lent for the bacteria infecting the patient) and had ne-
gative outcomes, but who did match the phage to the
There are many attributes of phages (see Table 1)
bacteria in subsequent trials and obtained positive out-
that would tend to favor a positive outcome in therapy.
Despite these attributes of phages, there were so
The solution. 1) Screen the bacteria infecting
many problems with the way phage therapy was prac-
a given patient against a panel of phages, to ensure that
ticed in the historical era that, by the time antibiotics
one of the phage strains will be lytic (analogous to the
were introduced in mid-century, it was already in sharp
“culture and sensitivity test” that physicians should per-
decline in the West. The investigators who developed
form; and 2) develop “multivalent” phages that lyse all
antibiotics did not make the kinds of mistakes exhibited
or most of the bacterial strains within a given species
R. M. Carlton: Phage Therapy in the Past and Future
Problem 2. Bacterial debris present in the phage prep-
exposed to bacteria or bacteriophages (and so would
not have antibodies). Moreover, the phages in Merril’s
The issue. Injection of even minute amounts of en-
experiment remained viable in the spleens of these ani-
dotoxin and other bacterial debris can be fatal to pa-
mals over a period of several days, indicating that they
tients. Unfortunately, many of the phage preparations
were neither neutralized by antibody nor engulfed by
used by practitioners in the historical era were crude
macrophages. Rather, they appeared to have been pas-
lysates. When these preparations were injected i.v., i.p.,
sively entrapped in (sequestered by) these filtering or-
and in some cases even intrathecally, any beneficial
gans. Such trapped phages would be unavailable to
effect of the phages would likely have been counter-
acted by illness and deaths resulting from the endo-
The solution. The author of this review collaborated
with investigators at the U.S. National Institutes of
The solution. Modern technology allows density
ERRIL et al.11) in the development of a method
centrifugation, banding, and other methods of purifica-
to isolate and amplify phage strains that are cleared at
a slower rate. We reasoned that in all species of phage,
minor variations in coat proteins might be present that
Problem 3. Attempts to remove host bacteria from ther-
would enable some variants to be less easily recognized
by the RES organs and to thereby remain in the circu-
The issue: In order to ensure that phage prepara-
lation for longer periods of time than the “average”
tions would not contain live bacteria, some early inves-
wild-type phage. In this “serial passage” method, the
tigators added mercurials and/or oxidizing agents,
wild-type preparation is injected into an animal, and
while others heated them. It is now known that such
then blood samples are taken at progressively longer
agents and procedures will denature or otherwise inac-
time points. Any phages found in the blood sample are
tivate the phage coat proteins. These investigators
grown to high titer and reinjected. Through iterative
did not check for continued viability of the phages.
rounds of passage, one can amplify the long-circulating
The false-negative results of such studies were the
strains being isolated. U.S. and PCT patents have been
unintended (but inevitable) consequence of such prac-
For coliphage lambda as well as for salmonella
The solution: Sterile filtration. If chemical agents
phage P22, phage variants were isolated in this manner
must be used, retitrate the preparation over time to en-
that were much longer-circulating than the wild-type.
For example, for every 100 000 particles of the wild--type lambda used at baseline, only one particle re-
mained in circulation at 18 h; whereas for the long-cir-
The issue. In fairness to phage investigators in the
culating phage mutant isolated at the 8th round of serial
historical era, at the time it was not an accepted prac-
passage, for every 100 000 injected, at 18 h 62 500 par-
tice, in any discipline, to conduct pharmacokinetic
ticles remained in circulation. For each moment of
studies. However, had the early phage investigators
time, far more of these long-circulating phages are pro-
conducted such studies, they would have discovered
pagating exponentially, as compared to the situation for
that bacteriophages (being foreign proteins) tend to be
rapidly cleared from the circulation. This clearance
As predicted, these long-circulating phages were far
problem was first documented by Merril and his col-
superior to the wild-types from which they were
leagues in 1973 who injected high titers of phage lamb-
derived, in terms of rescuing animals from an other-
da into non-immune germ-free mice. They discovered
wise-fatal fulminant bacteremia: 1) with no treatment,
that the phages were rapidly cleared by the spleen, liver
all animals were dead within 48 h; 2) treatment with
and other filtering organs of the reticulo-endothelial
the wild-type phages prevented death, but the animals
system (RES)7. This was a seminal observation, given
became critically ill (a human with such degrees of
Gunther Stent’s widely-accepted statement that one of
illness would be in the intensive care unit); and 3) in
the principal reasons phages had failed as a therapeutic
contrast, with administration of the long-circulating
was their supposed inactivation by pre-existing anti-
phage strain, the only sign of illness seen was mild
bodies to them. However, any clearance of the phages
lethargy. These results were published in the Proceed-
from the bloodstream of the germ-free animals used by
ings of the National Academy of Sciences (ref. 11✦), and
Merril and his group (ref.7) would not be due to anti-
were accompanied by a Commentary by Nobel laureate
bodies, since those animals had never previously been
R. M. Carlton: Phage Therapy in the Past and Future
We have elucidated the molecular basis of the mu-
Problem 7. Failure to establish scientific proof of effi-
tation in lambda that reduced its rate of clearance:
a single point mutation, an A to G transition, had oc-
In scholarly reviews of comparative styles of re-
curred in the gene encoding the major head protein E.
search, Dutch historian TON VAN HELVOORT has dis-
This mutation substituted a basic amino acid (lysine)
cussed d’Hérelle’s systematic failure to conduct
for an acidic one (glutamic acid), causing a double
double-blind studies. As van Helvoort pointed out,
charge shift readily seen on 2D gel electrophoresis.
while it is true that ethical problems are faced by
Computer modeling predicted that the mutation oc-
anyone who has to administer placebo to some patients
curred in a loop of the E protein that sticks out into
(in order to prove efficacy), nevertheless the investi-
space and that therefore may interact with the external
gators who later tested antibiotics did conduct double-
environment. A double charge shift in this region of
-blind, placebo-controlled trials. Van Helvoort points
a protein that is highly represented on the surface of the
out that, even when using phages to treat an epidemic
virion could conceivably alter the phage’s interaction
of diarrhea in poultry on a French farm, d’Hérelle
with the microcirculation of the spleen, in such a way
failed to use a placebo on half the flock (a situation
that the mutant phage is less easily entrapped than the
where ethical considerations would not have been an
issue). As a consequence, all reports of phage therapy’ssuccesses in the historical era were anecdotal. No sys-
tematic proof was available to demonstrate that the re-
The issue. It was not until the late 1950s that Lwoff
demonstrated the ability of some phage genomes to
integrate into the bacterial chromosome as “pro-
Problem 8. The scientific style of phage investigators
phages”. After a period of time (up to days or weeks,
or longer), such prophages can enter the lytic cycle, and
D’Hérelle’s failure to conduct placebo-controlled
will thus appear as plaques on a bacterial lawn. It is
studies, even on chickens, is an important example of
likely that some phage therapy trials in the historic era
his style. This story is a notable example of the nega-
had a negative outcome due to the inadvertent use of
tive impact an investigator’s personality can have on
phage strains that, being lysogens, could not provide
the outcome of a discovery, and d’Hérelle’s style con-
the rapid lysis and exponential growth in numbers that
trasts sharply to the strongly positive influence that
other scientists (such as Pasteur) have had on the out-
The solution. Use only phages that are lytic; se-
comes of their discoveries. Whereas Pasteur excelled at
quence phages that are strong candidates for clinical
conceiving of definitive experiments, and was persua-
trials, looking for (among other things) homologies to
sive in style, d’Hérelle failed to conduct definitive ex-
periments, and was antagonistic rather than persuasive.
For example, d’Hérelle maintained to the end that
phages are the sole mechanism of defense against bac-
The issue. There are reports in the literature20 that
terial infection. While he may have been correct in his
neutralizing antibodies appear a few weeks after ad-
view that epidemics can sometimes be checked by the
ministering phages to humans or animals. Given the
spontaneous appearance of a lytic strain of phage,
time lag, antibodies would not seem likely to interfere
nevertheless he was incorrect in categorically dismis-
with an acute treatment lasting a week or so. However,
sing the discoveries of Nobel laureates Metchnikoff and
in chronic treatment, or in treatment of a recurrence of
Ehrlich, who had shown that cellular elements (white
the same bacterial infection, the neutralizing antibodies
blood cells) and humoral elements (antibodies and
might prevent some proportion of the administered
complement) constitute the innate host defenses against
dose of phages from being able to adhere to the bac-
infection. D’Hérelle was afforded many opportunities
to integrate his discovery with those of Metchnikoff and
The solution. In treating chronic or recurrent
Ehrlich, but refused to the end (see below).
infections it may be possible to administer a higher
In addition to the damage he was doing to himself and
dose of phage, to compensate for those that are ren-
his cause with this adamance, d’Hérelle was attacked by
dered non-viable by interaction with neutralizing anti-
Nobel laureate Jules Bordet (for whom ✯Bordetella pertussis
bodies. In any case, the types and titers of antibodies
was named), who had an intense dislike not just for d’Hé-
that develop should be systematically studied in hu-
relle’s science but also for the man himself. Bordet used
his considerable influence to discredit D’H
R. M. Carlton: Phage Therapy in the Past and Future
D’Hérelle retreated from attacks by Bordet and
the phages grew exponentially in number, overwhelm-
others, and moved to Soviet Georgia in the 1930s (see
ref. 13✦). An ardent communist, he dedicated the last of
his published treatises to Josef Stalin. He was in Paris
Current Status of Human Phage Therapy Efforts
at the outbreak of World War II, refused to offer hisskills with phage therapy to the Germans*, and spent
Poland. Phage therapy is practiced in Poland, albeit
the occupation years in prison. By the time of the libera-
on a small scale. In the mid-1980s a series of papers
tion his health had been broken. He was invited to a post-
was published by a group led by the late Prof. S. S
War international scientific symposium, where colleagues
and his colleagues, including Dr. M. Mulczyk and Dr.
made a last effort to see if they could help him bridge the
B. Weber-Da˛browska, working at the L. Hirszfeld In-
gulf. He persisted in his belief that phages were the body’s
stitute of Immunology and Experimental Therapy (a
sole mechanism of defense against bacteria (“Ce n’est ✱que
branch of the Polish Academy of Sciences). These
la phage…”), and he died in isolation in 1949.
reported on 550 cases of suppurative bac-
Surely the prospects of phage therapy in the histori-
terial infections (empyemas, peritonitis, osteomyelitis,
cal era would have been better served if d’Hérelle had
etc.) in humans. Most of the cases were chronic; most
possessed some of the personality traits and scientific
were resistant to all available antibiotics; and most had
not been referred for this form of therapy until all elsehad failed, meaning that it was often quite late in the
Animal Models of Phage Therapy
The bacterial pathogens targeted included ✳Staphylococ-
From the 1950s to the 1980s there was little pub-
cus aureus, Pseudomonas aeruginosa, Klebsiella pneu-
lished on the subject of phage therapy. Then papers
moniae and E. coli. The phages used by these investigators
began to appear demonstrating the utility of phage ther-
are reported to have cured approximately 90% of the cases.
apy in animal models. For example, phages were shown
The criteria of cure were cessation of suppuration and,
to be effective in rescuing rats from fatal systemic in-
where applicable, complete closure of wounds/fistulae
fections (induced with E. coli✦)14 in rescuing calves and
(many of which had been draining for months).
These investigators administer phages orally, be-
rescuing chicks from fatal diarrhea (induced with S. ty-
cause they are aware of the hazards of administering
phimurium) , and in preventing destruction of skin
them parenterally (not all of the bacterial debris has
grafts in burned rabbits by Pseudomonas aeruginosa18.
been removed). They pre-treat the patients with anta-
As mentioned above M✭ERRIL et al.11 demonstrated in
cids and gelatin in order to protect the phages from
1996 that mice with fulminant E. coli bacteremia could
destruction by gastric acidity. These same investigators
be rescued by phages, and that long-circulating phage
have published evidence that phages administered
variants were superior to the wild-types (see below).
orally to humans in this manner do in fact reach the
In one of those studies cited, Smith and Huggins
(ref. 6✦) demonstrated that, in rats inoculated with a le-
The Polish investigators have been rigorous in
thal intramuscular dose of E. coli, a single injection of
matching the phages to the bacterial strain infecting the
a phage preparation was more effective than multiple
given patients. Their practice, as stated in the published
injections of antibiotics (chloramphenicol, tetracycline,
reports, is to culture the bacteria during the course of
etc.). This work was replicated in 1997 by LEVIN and
treatment, so that the occurrence of a mutant resisting
ULL , who used mathematical modeling in a popula-
the phage can be countered by switching to a different
tion dynamics approach to study the titers of phages
phage strain. The group also has panels of multivalent
and bacteria in the animals. The investigators con-
phages available, for use in fulminant infections (such
cluded that the reason a single injection of phage was
as septicemia with acute respiratory distress syndrome)
superior to multiple injections of antibiotics was that
where time is insufficient to classify the offending bac-
teria or to match phages to bacteria.
The group now has statistics on the treatment of
* The push of the German army into the region of Georgia was
approximately 1 300 cases. The overall cure rate across
intended not only to capture the region’s oil wells, but also to obtain
the spectrum of pathogens and sites of infection is ap-
the collection of phages manufactured at the Eliava-d’Hérelle In-
proximately 86% (personal communication from Dr.
stitute in Tblisi. That institute was providing phages to the Russian
❀ army, to control dysentery, Staphylococcus aureus infections of
❂ wounds, and other bacterial problems associated with war.
R. M. Carlton: Phage Therapy in the Past and Future
the absence of placebo controls means the power of
ance. Unfortunately, it has been demonstrated that some
suggestion cannot be definitively ruled-out. It is clear
hospital strains of methicillin-resistant ✳S. aureus (MRSA)
that the difficulties of that nation’s economy over recent
that are widespread have become vancomycin resistant
decades has denied the investigators the financial re-
upon exposure of the patients to vancomycin1, 2. Ex-
sources needed to enroll matched cohorts in a placebo
perts predict that S. aureus will progress to become
arm of a clinical trial. While the criticism is valid, and
completely resistant to vancomycin (the antibiotic of
absolute proof of principle can be obtained only
last resort for most strains of this pathogen), and that
through placebo-controlled trials, nevertheless the use-
when this occurs, millions of people will die each year
fulness of the data is improved by the detailed statistical
from infections that had until recently been fairly easy
accounting of the percentages of complete, partial and
to control. Based on such developments and impending
nil response. One of the factors that enables this author
developments with pathogens such as MRSA and VRE,
to find the data from Poland more believable (even in
opinion leaders have been warning that we are entering
the absence of double-blind proof) is that in conditions
such as emphysema where phage efficacy might be
While pharmaceutical companies are developing
somewhat impeded, the group’s statistics show that the
new antibiotics to counter the trend, it has been shown
success rate is considerably lower than for other condi-
that half a century of global antibiotic abuse has
tions where such impediments do not obtain*.
equipped the surviving bacteria with “supergenes” that
The Republic of Georgia. The work started in Tblisi
enable them to quickly resist new classes of antibiotics,
in the 1930s by d’Hérelle and his Georgian colleague,
even those to which they have never been exposed1.
Eliava, continues to this day. In the 1970s, under the
Examples of the “supergenes” are mutations that 1) en-
direction of Dr. Teimuraz Chanishvili, the Eliava-d’Hé-
able bacteria to pump out several classes of antibiotics
relle Institute had a large staff manufacturing consider-
(through an efficient efflux pump), or that 2) alter the
able quantities of phage preparations per year, primarily
antibiotic binding sites on ribosomal subunits, so that
for the control of dysentery in the troops of the Soviet
several different classes of antibiotics can no longer
Army. This group has anecdotal evidence of the effi-
inhibit those subunits. As a consequence, in recent
cacy of phage therapy. They report, for example, that
years, by the time newer antibiotics have gone through
in certain adult and pediatric hospitals it is routine for
clinical trials and have reached the market, 20% or
their phage preparations to be administered topically on
more of clinical isolates in the hospitals are already
surgical incisions. Given the lack of statistical analysis,
resistant to them at the time of regulatory approval, and
there is little to be said other than the anecdotal reports
within a few more years the majority of strains are re-
are encouraging that phage therapy can be useful.Multidrug-Resistant (MDR) Bacteria HaveFuture Prospects for Phage TherapyCreated a Need for Phage Therapy
Infectious disease experts have warned that there is
Several species of bacteria have become resistant to
now a compelling need to develop totally new classes of
most antibiotics, with some strains being resistant to all
antibacterial agents, ones that cannot be resisted by the
antibiotics. One example is vancomycin-resistant En-
same genes that render bacteria resistant to antibiotics.terococcusfaecium (VRE), a low-virulence pathogen
Phage therapy represents such a “new” class. We
that now frequently causes fatal bacteremias due to
believe that the impediments cited above (bacterial de-
complete resistance2. Another example is vancomycin
bris in the preparations, rapid clearance in the body,
intermediate-resistant ✳Staphylococcus aureus (VISA),
etc.) can be overcome, freeing up the phages so that
strains of which have recently emerged in three nations
their attributes (such as exponential growth, and the
(Japan, U.S. and Scotland), and are known to have
ability to mutate against resistant bacteria) can be used
killed 4 patients to date. Such strains spread throughout
Japanese hospitals within a year of their first appear-
There are 3 additional attributes of phages that
Host specificity. While the host specificity is some-
* Conditions where phage efficacy is predicted to be reduced
what of a drawback (requiring a matchup of phage to
would include 1) hypoxic sites, where bacterial replication is slower
bacterial target, and/or the development of highly
and therefore phage replication is reduced; and 2) chronic obstruc-
✾ tive pulmonary disease, where high acidity and proteases would be
multivalent phages), it also offers the great advantage
❇ expected to inactivate some percentage of the phages.
that the phages will not kill other species of bacteria.
R. M. Carlton: Phage Therapy in the Past and Future
Thus, e.g., phage therapy is not likely to kill off the
that are still susceptible to antibiotics, by helping to
healthy flora of the intestines, lungs or urogenital tract,
prevent the emergence of bacterial mutants against
and it is therefore unlikely to provoke the illnesses and
deaths seen when antibiotics cause overgrowth of pa-
thogens (such as Clostridia difficile and Candida albi-ReferencesGenetic engineering. It is possible to genetically en-
ryotes I: General properties of bacteriophages (chapter 7). Prac-
gineer phages to express new traits of potential value.
✾ tical applications of bacteriophages. CRC Press, Boca Raton,
In so doing, scientists will have to deal with the legit-
imate concerns of regulatory agencies concerning rec-
2. ALISKY J. et al. (1998): Bacteriophages show promise as anti-
ombinant organisms. The regulatory obstacles may be
❍ microbial agents. J. Infect., 36, 5–15.
well worth the price, given the powerful engineering
3. BARROW P. A. and SOOTHILL J. S. (1997): Bacteriophage ther-
❀ apy and prophylaxis: rediscovery and renewed assessment of
Ideal candidates for co-therapy with antibiotics. If
the potential. Trends Microbiol., 5, 268–271.
4. B❑ERCHIERI A. et al. (1991): The activity in the chicken alimen-
a given bacterium acquires resistance to a phage (e.g.
✾ tary tract of bacteriophages lytic for Salmonella typhimurium.
by a mutation in the receptor site or in the endonuclease
▲ Res. Microbiol., 142, 541–549.
enzymes), that mutation is not likely to “teach” the
5. D’HÉRELLE F. (1917): Sur un microbe invisible antagoniste des
bacterium to resist the antibiotics (which do not target
◆ bac. dysentériques. Crit. Rev. Acad. Sci. Paris, 165 373.
those structures). Similarly, if a given bacterium ac-
6. D’HÉRELLE F. (1922): The bacteriophage: its role in immunity.
❖ Williams and Wilkens Co. /Waverly Press, Baltimore, USA.
quires resistance to an antibiotic (e. g. by a mutation in
7. GEIER M., FRIGG M. E. and MERRIL C. (1973): Fate of bacte-
the reflux pump or in the ribosomal subunits), that mu-
riophage lambda in non-immune germ-free mice. Nature, 246,
tation is not likely to “teach” the bacterium to resist the
phage (which does not target those structures). Thus, if
8. LEDERBERG J. (1996): Commentary. Proc. Natl. Acad. Sci.
the bacterium is exposed to both agents, the odds are
USA, 93, 3167–3168.
remote that any resistance genes it starts to express (or
EVIN B. and BULL J. J. (1996): Phage therapy revisited: the
❙ population biology of a bacterial infection and its treatment
acquires anew) will enable it to survive. There are re-
❂ with bacteriophage and antibiotics. Am. Naturalist, 147, 881–898.
ports that bacteria tend to mutate against antibiotics
10. L❑EVY S. (1992): The antibiotic paradox. Plenum Press, New
once in every 106 divisions, while they tend to mutate
against phages once in every 107 divisions. Therefore
11. M❑ERRIL C. et al. (1996): Long-circulating bacteriophage as
the odds of a given bacterium mutating against a phage
❀ antibacterial agents. Proc. Natl. Acad. Sci. USA, 93, 3188–
and an antibiotic at the same time would be the product
12. MURRAY B. (1998): Diversity among multidrug-resistant En-
of 106×107, meaning it would likely take 1013 bacterial
✾ terococci. Emerging Infect. Dis., 4, 37–47.
divisions for such a double mutation to occur. Given
13. S❚HRAYER D. (1996): Felix d’Hérelle in Russia. Bull. Inst. Pas-
that low probability, the co-administration of phages
✾ teur, 94 91–96.
and antibiotics may help prevent the emergence of bac-
14. SMITH H. W. and H❋UGGINS R. B. (1982): Successful treatment
terial resistance to antibiotics, thereby greatly prolong-
❯ of experimental E. coli infections in mice using phage: its general
superiority over antibiotics. J. Gen. Microbiol., 128, 307–318.
15. SMITH H. W. and H❋UGGINS R. B. (1983): Effectiveness of
multiple classes of anti-HIV medications are adminis-
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